Hello list,

when a real number overflows the program halts with EInvalidOp error. How can I make the program behave the more standard way, where the variable gets the value "inf" and execution continues normally? This is vital for many tasks, like fractal computation.

example program:

current output:

desired output:

...

Thanks in advance,
Dimitris

P.S. Why when the program doesn't include the variants unit the program complains at runtime? What is that unit?

Dimitris,

when a real number overflows the program halts with EInvalidOp error. How can I make the program behave the more standard way, where the variable gets the value "inf" and execution continues normally? This is vital for many tasks, like fractal computation.

You can use try..except..end block and switch -Sd when compile:

program realover;
Uses math;
var r:real;
BEGIN
   r:=2;
   while True do
   begin
     try
       r:=r**2;
       writeLn(r);
     except
       r:=infinity;
       writeLn(r);
       // break
     end;
  end;
END.

Or you may take a look IEEE specification if it is necessary to create your own big float support for larger precision with fractals.

P.S. Why when the program doesn't include the variants unit the program complains at runtime? What is that unit?

At windows, it is not necessary for this example. Variants unit provide new type definition and supported functions, which can consist any simple type (integer, string, etc).

Sasa

> when a real number overflows the program halts with EInvalidOp error. > How can I make the program behave the more standard way, where the > variable gets the value "inf" and execution continues normally? This

is

> vital for many tasks, like fractal computation. You can use try..except..end block and switch -Sd when compile:

Thank you very much, this solves the problem though I think that performance-wise it is not optimal. What is the reason for freepascal being not IEEE-spec compliant? Is it backwards compatibility?

Or you may take a look IEEE specification if it is necessary to create your own big float support for larger precision with fractals.

It seems really weird that there is no such unit in the standard freepascal distribution. It would be a huge task for me to create one with C-like speed.

Dimitris

It is:
http://community.freepascal.org:10000/docs-html/rtl/math/setexceptionmask.html

You can turn off floating point exceptions using this procedure.

Thank you very much, this solves the problem though I think that performance-wise it is not optimal. What is the reason for freepascal being not IEEE-spec compliant? Is it backwards compatibility?

FPC is IEEE-spec compliant, since all computer follow up floating point standard. It should follow up to 80 bits for double-extended precision. Note that IEEE specification is recently under revision.

It seems really weird that there is no such unit in the standard freepascal distribution. It would be a huge task for me to create one with C-like speed.

That is specific task. Take a look Alex Fihman BigFloat unit, for example: http://www.db-access.com/

Sasa

Dimitrios Apostolou wrote

when a real number overflows the program halts with EInvalidOp error. How can I make the program behave the more standard way, where the variable gets the value "inf" and execution continues normally?

I'm not sure if overflow immediately results in infinity, I think first you get some denormalss. There's also nothing particularly standard about whether or not an exception is thrown when you have an FPU overflow, since all common FPU's I know about support both.

Anyway, you can mask overflow and related exceptions by doing this:

uses math;

...

SetExceptionMask([exDenormalized,exOverflow,exPrecision]);

Jonas

Jonas Maebe wrote

SetExceptionMask([exDenormalized,exOverflow,exPrecision]);

Thank you all for your answers, that will do just fine! Too bad though that it not that obvious in the documentation, which I browsed for many hours before posting to this list.

Thank you,
Dimitris